Baghdad, Iraq ? The Iraqi government, apparently unable to control its security agencies, said Tuesday that an armed government security unit had abducted an accredited Iranian diplomat in central Baghdad on Sunday. But the foreign minister couldn’t say where he was being held.

Iran accused the Ministry of Defense, which oversees the Iraqi army, of carrying out U.S. instructions in the abduction of the Iranian diplomat, Jalal Sharafi. The U.S. military denied any involvement.

“In all of our research we have found no unit within Multi-National Force-Iraq or that we are associated with that has conducted any operation that remotely resembles this,” said U.S. military spokesman Lt. Col. Christopher Garver. “We’re continuing to research based on the seriousness of this. However, at this time, there is no evidence that any MNF-I unit participated in this event.”

Iran’s accusations seemed to be the latest episode in what some Iraqi politicians called a cold war between the U.S. and Iran on Iraqi soil. In the last six weeks, U.S. forces have detained Iranian officials in Baghdad and in the Kurdish city of Irbil. On both occasions, the Iraqi government was unaware of the detentions. The Iraqi government said the men were in Iraq on official government business.

The Iraqi government had at best incomplete answers to questions Tuesday. Hoshyar Zebari, the Iraqi foreign minister, said the diplomat was driving through a central Baghdad neighborhood when he and his guards came under fire from men in vehicles that belonged to an Iraqi “government entity.”

Iraqi police, suspicious of the assault, intervened and seized four gunmen and one vehicle, Zebari said. After interrogating the four men, Iraqi authorities concluded that the gunmen were linked to an Iraqi government body, he said. But Zebari couldn’t say where the diplomat was taken or where he’s being held.

He left no doubt that the government was embarrassed by the abduction.

“We are working very hard and the prime minister is working very hard to get to the bottom of this,” Zebari said. “This is unacceptable. It’s our responsibility to protect diplomats in this country.”

Iraqi government spokesman Ali al Dabbagh declined to comment, with his secretary saying he wasn’t briefed on the details of the incident.

Security crackdown

Prime Minister Nouri al-Maliki complained Tuesday the long-awaited Baghdad security operation was off to a slow start, but he also reassured Iraqis that security forces will live up to their responsibilities.

The statement came as new checkpoints were erected and increased vehicle inspections and foot patrols were reported in some neighborhoods – providing the main evidence so far that U.S. and Iraqi forces were gearing up for a major neighborhood-to-neighborhood sweep to quell sectarian violence in the city of 6 million.

At least 51 Iraqis also were killed or found dead around the country on Tuesday, including eight slain by two car bombs in Baghdad.

“The operations will unite us and we will take action soon, God willing, even though I believe we’ve been very late and this delay has started to give a negative message,” al-Maliki said in a meeting with military commanders shown on state TV.

“I hope that more efforts will be exerted and more speed exerted in carrying out and achieving all the preparations to start the operations,” he said.